It's such a simple thing, the key to making a good comic book adaptation: don't mess too much with the source material. Whenever one doesn't work it's usually because of needless changes and compromises, a basic lack of respect for the origins of the whole endeavour, as if comics are just, you know, for kids. Of course, bringing a great actor on board is equally important and Robert Downey Jr, still enjoying his glorious rehabilitation from movie jail, is certainly up to the task. He takes such complete ownership of the role and the movie, his performance never lets you lose sight of arms dealer/inventor Tony Stark, even when it's an iron-clad CGI substitute. It's up to any decent superhero movie to sell you the more outlandish concepts, not alter them to fit. Here, Downey makes you believe he can walk away from a crash landing, or make a robo suit out of scraps in a cave. He even makes a likable arms dealer, which is as impressive as any of the state-of-the-art effects work. The DVD and Blu-Ray disc are as slick and high tech as you'd expect but also unusually informative, with screen tests, commentary, artwork and in-depth documentaries on the special effects and comic-book roots. po'n